In a typical printer, media trays store media sheets within the printer. During the printing cycle, a media transport system retrieves media sheets from a tray, routes the media through the printer to receive an image, and then ejects the media into an output tray for collection by a user. The media transport system utilizes drive rollers and idler rollers to transport media through the printing process. Drive rollers are fixedly mounted about shafts that are coupled to the rotational output of an electrical motor or other actuator. As the shafts rotate in response to the rotational output of a motor, the drive rollers also rotate. Idler rollers are mounted for rotation about an idler shaft that is engaged to a printer surface. Typically, the idler rollers are positioned opposite drive rollers, and a biasing member acting on an idler shaft presses the idler rollers against the drive rollers. As the drive rollers rotate, they frictionally engage the idler rollers sufficiently to rotate the idler rollers. As a media sheet contacts a drive roller and idler roller junction, known as a nip, the rotating rollers propel the sheet through the media path. Thus, the idler rollers assist in the movement of media sheets through the printer without requiring additional actuators for their rotation.
Idler shafts are secured to the printer surface in various ways that enable the shafts to move in a direction normal to the surface of the media to compensate for media sheets of different thicknesses that may be retrieved from different trays. To illustrate, consider that the idler rollers and the drive rollers contact one another in the absence of a media sheet in the nip. As a media sheet enters the nip, the thickness of the media forces the idler roller to separate from the drive roller. After the sheet exits the nip, the idler roller drops to its previous position to reengage the drive roller. Thus, the floating attachment of the idler shaft to the printer surface enables the idler roller to compensate for media sheets of different thicknesses.
One example of such a floating attachment fits the terminal ends of an idler shaft within slotted brackets having two opposing sidewalls, while a biasing member, such as a spring, urges the shaft against a printer surface. In this arrangement, the sidewalls limit the movement of the idler shaft in a direction parallel to the direction of media travel. The shaft is free to move in a direction normal to the media surface, subject to the urging of the biasing member, which helps hold the shaft within the bracket. While this structure helps effectively form a media nip for transporting media along a path, it also permits an idler shaft to strike the slotted bracket sidewalls intermittently in response to vibrations exhibited by other printer components. For example, motors, belts, and even the rotation of idler rollers upon startup, may cause an idler shaft to vibrate within a bracket. Furthermore, the structures to which the brackets are connected may amplify the vibrations and generate objectionable noise.
The materials used to manufacture the idler shaft, bracket, and biasing member may at times also contribute to the generation of undesirable noise. Manufacturers may construct the idler shaft and the brackets from any number of materials, but often rigid plastic is used for its workability and durability. However plastic-to-plastic interfaces, such as the contact points between the shaft and the bracket, are susceptible to generating noise when the rigid materials vibrate and impact one another. Furthermore, the above described vibrations may also contribute to the generation of noise at the biasing member and idler shaft interface, because manufacturers often construct the biasing member of a rigid material. Of course, these noise sources do not decrease the functionality of the printer, but some users may prefer a quieter printer.
In order to eliminate the vibration, and any noise that may arise from such vibrations, manufacturers have looked to various vibration dampening methods. For example, biasing springs may force the idler shaft to one side of the bracket in an effort to reduce the associated “chatter” between the idler shaft and the bracket. This complicated system requires the selection of a biasing means of sufficient strength to reduce chatter without unnecessarily restricting the desired movement of the shaft. Simpler vibration dampening systems are therefore desirable.